[scardine]

You must watch the documentary "The secret life of babies". There is a scene where they put several babies on a "cliff" situation (with a glass in the same level to prevent them falling), they will confidently march into the glass - they do several other experiments that prove babies are fearless.

https://www.netflix.com/title/80009352

[giardini]

Babies are not born afraid of the cliff (i.e., it isn't hardwired into the infant brain); they develop fear of it at about 9 months' age, once their depth perception has developed.